The long range goal of this research is to promote an understanding of the mechanisms by which a eukaryotic cell, starting with genetic material, manages to synthesize functional gene products. The particular gene products to be studied are yeast tRNAs. Research efforts are directed towards isolating conditional mutants defective in tRNA transcription and/or maturation in order to determine: a) the organization of tRNA genes on the yeast chromosome; b) which RNA polymerases and polymerase subunits function in yeast tRNA transcription; c) the nature of the tRNA primary transcript; d) what biochemical steps are involved in the maturation of the initial tRNA transcript to a functional tRNA. We have started to characterize one conditional mutant (ts136) which accumulates tRNA precursors and 2 mutants which synthesize less mature tRNA. Future research efforts will be: a) to further study mutant ts136 so as to identify specific tRNAs contained in the precursor molecules. b) to determine the relationship of specific precursor tRNAs found in ts136 to the mature tRNAs which they contain. We hope to characterize the number of excess nucleotides, their location (i.e. 5' and/or 3'), and sequence of given precursor tRNAs. c) to determine the biochemical defects of ts136 and other mutants which we have obtained so as to study the steps involved in the processing of precursor tRNA. d) and, to obtain additional mutants defective at other steps in tRNA processing and/or transcription. BIBLIOGRAPHIC REFERENCES: Hopper, Anita K., and Banks, Fred. "Maturation of tRNA in the Eukaryote Saccharomyces cerevisiae"; Abstracts American Society of Microbiology Meeting 1977, in press. Andrew, C.; Hopper, Anita K., and Hall, B.D. "A Yeast Conditional Mutant Defective in the Maturation of 25S rRNA"; Mol. Gen. Genet. 144: 29-37, 1976.